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17 pages, 3701 KiB

Open AccessArticle

Study of the Pozzolanic Reactivity of Sugar Cane Straw Ashes (SCSA) Burned under Controlled Conditions

by Michelle S. Rodrigues, Jordi Payá, Lourdes Soriano, José Monzó, María Victoria Borrachero, Holmer Savastano, Jr. and Antonio L. Beraldo

Materials 2023, 16(21), 6841; https://doi.org/10.3390/ma16216841 - 24 Oct 2023

Cited by 2 | Viewed by 908

Abstract

The aims of this work were to evaluate the reactivity of sugarcane straw ashes (SCSA) burned under controlled conditions and to analyze their reactivity in blended cement and hydrated lime pastes by thermogravimetric analysis (TG) and calorimetry. Four different ashes were produced, and [...] Read more.

The aims of this work were to evaluate the reactivity of sugarcane straw ashes (SCSA) burned under controlled conditions and to analyze their reactivity in blended cement and hydrated lime pastes by thermogravimetric analysis (TG) and calorimetry. Four different ashes were produced, and burned at 600 °C, 700 °C, 800 °C and 900 °C (SCSA600, SCSA700, SCSA800 and SCSA900, respectively). These ashes were characterized by X-ray fluorescence spectroscopy, X-ray diffractometry, particle size distribution by laser diffraction and specific area surfaces to assess their potential interest in the partial replacement of inorganic binders (Portland cement (OPC) and hydrated lime). The hydrated lime pastes were subjected to scanning electron microscopy (SEM) and TG. The blended cement pastes were analyzed by TG and calorimetry, compressive strength testing and mercury intrusion porosimetry. High lime fixation percentages were observed in the hydrated lime and OPC pastes and were higher than 75% and 50% for the ashes burned at 600 °C and 700 °C, respectively. Calorimetry showed a delay in the heat release of SCSA600 and SCSA700 compared to the control paste. These pastes also had higher compressive strength and a smaller total pore volume. The results indicate the positive response of preparing sugar cane ashes under controlled conditions (mainly for straw calcined within the 600–700 °C range) for their use as pozzolanic addition by partially replacing inorganic binders. Full article

(This article belongs to the Special Issue Microstructural, Mechanical, and Durability Characteristics of Cementitious Materials)

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22 pages, 5224 KiB

Open AccessArticle

Residual Properties of Geopolymer Concrete for Post-Fire Evaluation of Structures

by Balamurali Kanagaraj, Nammalvar Anand, Diana Andrushia and Venkatesh Kodur

Materials 2023, 16(17), 6065; https://doi.org/10.3390/ma16176065 - 4 Sep 2023

Cited by 2 | Viewed by 1049

Abstract

The research focuses on effectively utilizing industrial by-products, namely fly ash (FA) and ground granulated blast furnace slag (GGBS), to develop sustainable construction materials that can help reduce carbon emissions in the construction industry. Geopolymer mix design using these by-products is identified as [...] Read more.

The research focuses on effectively utilizing industrial by-products, namely fly ash (FA) and ground granulated blast furnace slag (GGBS), to develop sustainable construction materials that can help reduce carbon emissions in the construction industry. Geopolymer mix design using these by-products is identified as a potential solution. The study investigates the impact of different water to binder ratios (W/B) ranging from 0.4 to 0.6 on the residual properties, including compressive strength (CS), of geopolymer concrete (GPC), in accordance with Indian Standard for Alkali activated concrete. Lower W/B ratios were found to result in a more compact and less porous microstructure in the GPC. Additionally, the research explores the post-fire performance of GPC with varying grades (M10, M20, M30, & M40) and different W/B ratios, following the ISO 834 standard fire curve. It was observed that concrete samples exposed to elevated temperatures displayed a more porous microstructure. The mass loss of GPC with 0.4 W/B was found to be 2.3–5.9% and for 0.6 W/B ratio, the loss was found to be 3–6.5%, after exposing to 30-, 60-, 90-, and 120-min of heating. In the case of strength loss, for 0.4 W/B ratio, the loss was 36.81–77.09%, and for 0.6 W/B ratio the loss was 38.3–100%, after exposing to 30-, 60-, 90-, and 120-min of heating. Overall, the findings suggest that optimizing the W/B ratio in geopolymer concrete can enhance its compressive strength, as well as residual properties, and contribute to its suitability as a sustainable construction material. However, the response to elevated temperatures should also be considered to ensure its performance in fire scenarios. Full article

(This article belongs to the Special Issue Microstructural, Mechanical, and Durability Characteristics of Cementitious Materials)

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13 pages, 6191 KiB

Open AccessArticle

Full Characterization of Self-Compacting Concrete Containing Recycled Aggregates and Limestone

by Meriem Guessoum, Fouad Boukhelf and Fouzia Khadraoui

Materials 2023, 16(17), 5842; https://doi.org/10.3390/ma16175842 - 26 Aug 2023

Viewed by 1136

Abstract

This work deals with the study of self-compacting concretes (SCCs) containing recycled aggregates (RAs) recovered from demolition waste and limestone filler as a partial replacement for natural aggregates (NAs) and cement, respectively. Four mix designs were developed and characterized in both the fresh [...] Read more.

This work deals with the study of self-compacting concretes (SCCs) containing recycled aggregates (RAs) recovered from demolition waste and limestone filler as a partial replacement for natural aggregates (NAs) and cement, respectively. Four mix designs were developed and characterized in both the fresh and hardened states. In the fresh state, the properties studied included slump, sieve stability, and t₅₀₀ viscosity. In the hardened state, the properties studied were compressive strength and porosity at 15 h and 28 days, thermogravimetric analysis, and durability tests involving freeze–thaw cycles and accelerated carbonation. The results indicate the RAs lead to a decrease in slump flow. However, the substitution rate of aggregate replacement does not affect the compressive strength. This can be attributed to the optimized mix design, resulting in all SCC mixtures achieving the same compressive strength class of 30–35 MPa. As for the durability tests, the incorporation of recycled aggregates modifies the behavior of the concrete during freeze–thaw cycles. Throughout the 300 freeze–thaw cycles, all concrete mixtures exhibited a mass loss accompanied by a slight strain increase, but the materials remained visually intact. Additionally, the carbonation depth is strongly influenced by the rate of aggregate replacement due to changes in the microstructure, particularly in porosity. Full article

(This article belongs to the Special Issue Microstructural, Mechanical, and Durability Characteristics of Cementitious Materials)

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17 pages, 6833 KiB

Open AccessArticle

Effect of Ultrafine Cement (UFC) on the Corrosion Resistance of Cement Soil in Peat Soil Environment

by Yongfa Guo, Jing Cao, Huafeng Sun, Wenyun Ding, Guofeng Hua, Wei Wei and Siyang Huang

Materials 2023, 16(16), 5520; https://doi.org/10.3390/ma16165520 - 8 Aug 2023

Viewed by 1125

Abstract

Many peat soils are distributed around plateau lakes, and the reinforcement of peat soils with high organic matter content by ordinary cement cannot meet the actual engineering requirements. In order to obtain better mechanical properties and durability of the reinforcement, this experiment prepared [...] Read more.

Many peat soils are distributed around plateau lakes, and the reinforcement of peat soils with high organic matter content by ordinary cement cannot meet the actual engineering requirements. In order to obtain better mechanical properties and durability of the reinforcement, this experiment prepared peat soil by mixing humic acid reagent into the alluvial clay soil with low organic matter content. The cement soil samples were prepared by adding cement and ultrafine cement (UFC) by stirring method; the samples were then soaked in fulvic acid solution to simulate the cement soil in the peat soil environment. Using the unconfined compressive strength (UCS) test, scanning electron microscope (SEM) test, and pores and cracks analysis system (PCAS) test, the effect of UFC content change on cement soil’s humic acid erosion resistance was explored, and the optimal UFC content range was sought. The results of the UCS test show that with an increase in immersion time, the strength curves of cement soil samples gradually increase to the peak strength and then decrease. Significant differences in the time correspond to the peak strength, and the overall presentation is two processes: the strength enhancement stage and the corrosion stage of the sample. The incorporation of UFC makes the cement soil in the peat soil environment exhibit excellent corrosion resistance, and the optimal UFC content is 10%. The results of the SEM and PCAS tests show that the microstructure of cement soil after immersion time exceeds 90 days, increases with an increase in immersion time, and its structural connectivity gradually weakens. The excellent characteristics of UFC particles, such as small particle size, narrow particle size distribution, fast hydration reaction rate, high hydration degree, and many hydration products, weakened the adverse effects of humic acid on the cement soil structure to a certain extent. Therefore, although the number of macropores increases, they are not connected. It still presents a relatively compact honeycomb overall structure, which correlates well with the UCS results. Full article

(This article belongs to the Special Issue Microstructural, Mechanical, and Durability Characteristics of Cementitious Materials)

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19 pages, 3618 KiB

Open AccessArticle

Assessment of Properties of Structural Lightweight Concrete with Sintered Fly Ash Aggregate in Terms of Its Suitability for Use in Prestressed Members

by Małgorzata Rodacka, Lucyna Domagała and Rafał Szydłowski

Materials 2023, 16(15), 5429; https://doi.org/10.3390/ma16155429 - 2 Aug 2023

Cited by 4 | Viewed by 1216

Abstract

The main aim of the paper was to assess whether the lightweight concrete with a new type of sintered fly ash aggregate can be used as a structural material for post-tensioned elements subject to high effort. This purpose was achieved by comparison of [...] Read more.

The main aim of the paper was to assess whether the lightweight concrete with a new type of sintered fly ash aggregate can be used as a structural material for post-tensioned elements subject to high effort. This purpose was achieved by comparison of the properties of lightweight aggregate concrete with Certyd aggregate (LWAC) and normal-weight concrete with dolomite aggregate (NWAC) of similar strength in terms of their suitability for use in prestressed members. Special emphasis was placed on long-term, relatively rarely performed tests of rheological properties such as shrinkage and creep. The research was conducted on standard specimens as well as on plain and post-tensioned beams of bigger scale, which could reflect better the behavior of the materials in a destined type of structural members. The carried out tests showed that, despite the expected lower density and modulus of elasticity, LWAC revealed comparable tensile strength and lower shrinkage and creep in the whole time of observations (ca 1.5 years) in comparison to NWAC. Moreover, the total loss of prestressing force for beams made of LWAC was slightly lower than for NWAC. Estimations of tensile strength and modulus of elasticity values according to the standard Eurocode EN-1992-1-1 for both concrete types turned out to be satisfactory. However, the rheological properties of the tested lightweight concrete seemed to be considerably overestimated. Full article

(This article belongs to the Special Issue Microstructural, Mechanical, and Durability Characteristics of Cementitious Materials)

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30 pages, 13991 KiB

Open AccessArticle

Effect of Imperial Smelting Process Slag Addition in Self Compacting Concrete Concrete on the Efficiency of Electrochemical Chloride Extraction

by Zofia Szweda, Janusz Mazurkiewicz, Petr Konečný and Tomasz Ponikiewski

Materials 2023, 16(14), 5159; https://doi.org/10.3390/ma16145159 - 21 Jul 2023

Cited by 3 | Viewed by 859

Abstract

This paper presents the analysis of how ISP slag addition affects the effectiveness of chloride extraction from self-compacting concrete. Corrosion processes were initiated by chloride ions added to concrete by the method accelerated with an electric field. Corrosion of reinforcement was monitored using [...] Read more.

This paper presents the analysis of how ISP slag addition affects the effectiveness of chloride extraction from self-compacting concrete. Corrosion processes were initiated by chloride ions added to concrete by the method accelerated with an electric field. Corrosion of reinforcement was monitored using the method of linear polarization resistance (LPR). Polarization measurements of steel reinforcement and chloride profiles were analysed to evaluate the effectiveness of electrochemical extraction. Microstructural analysis was conducted on a specimen of concrete after migration and extraction of chlorides. The presence of chloride ions and the application of an electric field during migration were tested with respect to the changed microstructure of concrete evaluated on the basis of image analysis using a scanning electron microscope (SEM). The research contributes to a better understanding of the corrosion processes caused by the presence of chloride ions in concretes in which ISP slag was used as a substitute for sand in various amounts. Thanks to the treatments of concrete with already corroding reinforcement bars, it can be concluded that the moderate replacement of sand with ISP slag limited to 25% allows for the effective inhibition of corrosion processes taking place in these concretes. However, it is not possible to completely withdraw already started corrosion processes in steel. The observations of the microstructure of concrete in which sand was completely replaced with ISP slag indicate that after prolonged use of the chloride extraction process, we can expect a change in the microstructure and the formation of ettringite, which may cause the concrete structure to burst. The obtained information will contribute to the development of modelling methods for chloride ion extraction from a wide range of currently used concretes. Full article

(This article belongs to the Special Issue Microstructural, Mechanical, and Durability Characteristics of Cementitious Materials)

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11 pages, 3034 KiB

Open AccessArticle

Experimental Research on the Energy Evolution of Concrete under Impact Loading

by Huan Wang, Faning Dang, Jie Ren, Yanjun Li and Lin Zhu

Materials 2023, 16(14), 5140; https://doi.org/10.3390/ma16145140 - 21 Jul 2023

Cited by 2 | Viewed by 752

Abstract

This paper presents an experimental study on the dynamic strength of concrete by using a split Hopkinson pressure bar. The stress–strain relationship and fragmentation degree of concrete were analyzed. The change process of the incident energy, reflection energy, transmission energy and consumption energy [...] Read more.

This paper presents an experimental study on the dynamic strength of concrete by using a split Hopkinson pressure bar. The stress–strain relationship and fragmentation degree of concrete were analyzed. The change process of the incident energy, reflection energy, transmission energy and consumption energy of concrete was calculated. The corresponding relationship between the variation of each energy and the stress state of concrete was studied. The law of energy evolution during the concrete fracture process was determined and the mechanism of concrete dynamic strength increase was revealed from the perspective of energy. The results show that the higher the strain rate, the higher the fragmentation degree of concrete, the smaller the grain diameter of fragments, the easier cracks are to pass directly through the aggregate, and the more regular the fragment shape. The change process of increasing amplitude of concrete consumption energy can reflect four mechanical states of concrete: stress increase, stress slow releasing, stress rapid releasing, and return-to-zero stress. Since the increase in reflected energy does not increase immediately with the increase in strain rate, it leads to the hysteresis of energy release in concrete, resulting in an increase in the dynamic strength of concrete. Full article

(This article belongs to the Special Issue Microstructural, Mechanical, and Durability Characteristics of Cementitious Materials)

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16 pages, 4729 KiB

Open AccessArticle

Development of Cemented Paste Backfill with Superfine Tailings: Fluidity, Mechanical Properties, and Microstructure Characteristics

by Yafei Hu, Keqing Li, Bo Zhang and Bin Han

Materials 2023, 16(5), 1951; https://doi.org/10.3390/ma16051951 - 27 Feb 2023

Cited by 10 | Viewed by 1625

Abstract

Previous studies have shown that the effectiveness of superfine tailings cemented paste backfill (SCPB) is influenced by multiple factors. To optimize the filling effect of superfine tailings, the effects of different factors on the fluidity, mechanical properties, and microstructure of SCPB were investigated. [...] Read more.

Previous studies have shown that the effectiveness of superfine tailings cemented paste backfill (SCPB) is influenced by multiple factors. To optimize the filling effect of superfine tailings, the effects of different factors on the fluidity, mechanical properties, and microstructure of SCPB were investigated. Before configuring the SCPB, the effect of cyclone operating parameters on the concentration and yield of superfine tailings was first investigated and the optimal cyclone operating parameters were obtained. The settling characteristics of superfine tailings under the optimum cyclone parameters were further analyzed, and the effect of the flocculant on its settling characteristics was shown in the block selection. Then the SCPB was prepared using cement and superfine tailings, and a series of experiments were carried out to investigate its working characteristics. The flow test results showed that the slump and slump flow of SCPB slurry decreased with increasing mass concentration, which was mainly because the higher the mass concentration, the higher the viscosity and yield stress of the slurry, and thus the worse its fluidity. The strength test results showed that the strength of SCPB was mainly affected by the curing temperature, curing time, mass concentration, and cement-sand ratio, among which the curing temperature had the most significant effect on the strength. The microscopic analysis of the block selection showed the mechanism of the effect of the curing temperature on the strength of SCPB, i.e., the curing temperature mainly affected the strength of SCPB by affecting the hydration reaction rate of SCPB. The slow hydration process of SCPB in a low temperature environment leads to fewer hydration products and a loose structure, which is the fundamental reason for the strength reduction of SCPB. The results of the study have some guiding significance for the efficient application of SCPB in alpine mines. Full article

(This article belongs to the Special Issue Microstructural, Mechanical, and Durability Characteristics of Cementitious Materials)

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20 pages, 11597 KiB

Open AccessArticle

The Effect of Cementitious Materials on the Engineering Properties and Pore Structure of Concrete with Recycled Fine Aggregate

by Zihao Liu, Koji Takasu, Hiroki Suyama, Hidehiro Koyamada, Shilun Liu and Qi Hao

Materials 2023, 16(1), 305; https://doi.org/10.3390/ma16010305 - 28 Dec 2022

Cited by 6 | Viewed by 1999

Abstract

With the rapid development of urbanization, the construction industry consumes a lot of cement and produces a large amount of construction waste. To overcome this situation, the rational use of recycled aggregate produced from waste concrete is one of solutions. In some countries, [...] Read more.

With the rapid development of urbanization, the construction industry consumes a lot of cement and produces a large amount of construction waste. To overcome this situation, the rational use of recycled aggregate produced from waste concrete is one of solutions. In some countries, the building industry has approved the use of recycled coarse aggregates in concrete, with some limits. However, practically all existing standards and regulations prohibit the use of recycled fine aggregate (RFA) in concrete. Therefore, study on improving the performance of RFA concrete is vital. In this study, the effects of fly ash and GGBS on concrete with RFA were investigated. Compressive strength, pore structure, drying shrinkage and accelerated carbonation were tested. The correlation between the pore structure and properties of concrete was analyzed. The results show that adding fly ash and GGBS to RFA concrete increased its compressive strength, modified pore structure, reduced drying shrinkage, and even achieved higher compressive strength and lower drying shrinkage than normal concrete. The compressive strength was mainly affected by the capillary pores, and the carbonation was mainly affected by the gel pores. Full article

(This article belongs to the Special Issue Microstructural, Mechanical, and Durability Characteristics of Cementitious Materials)

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15 pages, 4830 KiB

Open AccessArticle

Experimental Study on the Stability and Distribution of Air Voids in Fresh Fly Ash Concrete

by Yanhai Wang, Hang Lu, Rui Xiao, Wei Hu and Baoshan Huang

Materials 2022, 15(23), 8332; https://doi.org/10.3390/ma15238332 - 23 Nov 2022

Cited by 3 | Viewed by 1553

Abstract

The air void system purposely introduced by an air-entraining admixture (AEA) is of great significance for the protection of concrete from freeze–thaw damage. Fly ash has been globally used in concrete, while the unburnt carbon in fly ash can adsorb AEA molecules and, [...] Read more.

The air void system purposely introduced by an air-entraining admixture (AEA) is of great significance for the protection of concrete from freeze–thaw damage. Fly ash has been globally used in concrete, while the unburnt carbon in fly ash can adsorb AEA molecules and, thus, increase the AEA demand. Previous studies primarily focused on the air content of fresh fly ash concrete. This paper aimed to explore the stability and distribution of air voids in fly ash concrete at the fresh state. To achieve this goal, eleven different fresh fly ash concrete mixtures with an initial air content of 6 ± 1% were prepared in the laboratory. Samples were taken at various times within 75 min after initial mixing to investigate the air content and air void distribution in fly ash concrete at the fresh state using a super air meter (SAM). The results indicated that there was no significant correlation between loss on ignition (LOI) of fly ash and AEA demand to achieve the initial air content of 6 ± 1%. Class C fly ash concrete tended to have a better air content retention than Class F fly ash concrete. Compared with LOI, AEA demand had a stronger correlation with air content retention. Most of the fly ash concrete mixtures had a satisfactory air void system immediately after mixing, but the SAM number showed an increasing trend over time, suggesting the coarsening of the air void system with time. Full article

(This article belongs to the Special Issue Microstructural, Mechanical, and Durability Characteristics of Cementitious Materials)

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27 pages, 6311 KiB

Open AccessArticle

Effect and Mechanism of Metakaolin Powder (MP) on Rheological and Mechanical Properties of Cementitious Suspension

by Hengrui Liu, Zezhu Wang, Zhenghong Tian, Jingwu Bu and Jianchun Qiu

Materials 2022, 15(16), 5797; https://doi.org/10.3390/ma15165797 - 22 Aug 2022

Cited by 4 | Viewed by 1505

Abstract

The effects of metakaolin powder (MP) on the microscopic rheological properties and macroscopic flow parameters of cementitious suspension under various water–cement ratios were investigated. By analyzing the changes in the bonding strength coefficient and water film thickness (WFT), the mechanism of MP on [...] Read more.

The effects of metakaolin powder (MP) on the microscopic rheological properties and macroscopic flow parameters of cementitious suspension under various water–cement ratios were investigated. By analyzing the changes in the bonding strength coefficient and water film thickness (WFT), the mechanism of MP on flow and rheological parameters can be explored. Further, the effect of MP on mechanical properties was explained from the perspective of water absorption kinetics and hydration activity contribution rate. The incorporation of MP can reduce the flow rate and flow spread and increase the compressive strength, plastic viscosity, yield stress and thixotropy, and the effects of MP were distinctive under various W/CM ratios. The bonding strength coefficient and WFT increased and decreased with increasing MP replacement content, respectively. The regression analysis results revealed that the bonding strength coefficient and WFT were the most important factors influencing the macroscopic flow parameters and rheological parameters, which indicated that MP influenced the rheology and flowability of cementitious suspension by affecting the flocculent structure and particle distance. Compared with WFT, the bonding strength coefficient had a stronger effect on these parameters. The MP improved the compressive strength by reducing the average pore size and porosity and increasing the pore uniformity and hydration activity contribution rate of hardened paste, and this improvement was enhanced by increasing curing age. Full article

(This article belongs to the Special Issue Microstructural, Mechanical, and Durability Characteristics of Cementitious Materials)

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13 pages, 6096 KiB

Open AccessArticle

Experimental Research on Flexural Mechanical Properties of Ultrahigh Strength Concrete Filled Steel Tubes

by Xiaojun Zhou, Yulin Zhan, Tingmin Mou and Zhilun Li

Materials 2022, 15(15), 5262; https://doi.org/10.3390/ma15155262 - 29 Jul 2022

Cited by 5 | Viewed by 1339

Abstract

Based on the project of the Guansheng Qujiang Bridge, the flexural mechanical properties of an ultrahigh strength concrete filled steel tube (UHSCFST) were discussed. A total of six UHSCFST beam specimens were tested, and the cube strength (f_cu) of the [...] Read more.

Based on the project of the Guansheng Qujiang Bridge, the flexural mechanical properties of an ultrahigh strength concrete filled steel tube (UHSCFST) were discussed. A total of six UHSCFST beam specimens were tested, and the cube strength (f_cu) of the core concrete reached 80.3–115.2 MPa. The effects of concrete strength on flexural bearing capacity, deformation characteristics, and failure modes of UHSCFST specimens were discussed. Test results showed that the bending failure modes of UHSCFST specimens were the same as those of ordinary ones. The failure of UHSCFST specimens was attributed to excessive deflection, and local buckling occurred in the compression zone. Moreover, the bending capacity of the specimens did not decrease, even if they had yielded. Although ultrahigh strength concrete was poured, all of the specimens displayed outstanding bending ductility. The main function of core concrete was to provide radial restraint for the steel tube to avoid premature buckling. When the steel content of the specimen section was constant, the strength increases of core concrete had a slight impact on the bending failure mode, bearing capacity and ductility of UHSCFST specimen. The research results can deepen the understanding of the mechanical behaviors of the UHSCFST composite truss structure. Full article

(This article belongs to the Special Issue Microstructural, Mechanical, and Durability Characteristics of Cementitious Materials)

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13 pages, 6182 KiB

Open AccessArticle

Effect of Sulfur Content in Sulfate-Rich Copper Tailings on the Properties of MgO-Activated Slag Materials

by Peiyuan Chen, Fan Yang, Xin Qian, Yi Fang, Jin Li, Xueyan Chen and Yonghui Wang

Materials 2022, 15(12), 4340; https://doi.org/10.3390/ma15124340 - 20 Jun 2022

Cited by 3 | Viewed by 1696

Abstract

The high-value utilization of sulfate-rich tailings (SRCTs) can accelerate their mass consumption, so the many problems caused by the massive accumulation of SRCTs can be alleviated, such as environmental pollution, land occupation, security risk, etc. This study proposes using SRCTs to replace fine [...] Read more.

The high-value utilization of sulfate-rich tailings (SRCTs) can accelerate their mass consumption, so the many problems caused by the massive accumulation of SRCTs can be alleviated, such as environmental pollution, land occupation, security risk, etc. This study proposes using SRCTs to replace fine natural aggregates in MgO-activated slag materials (MASMs) and investigate the influence of the sulfur content in SRCTs on the properties of MASMs. The experimental results showed that the 28 d compressive strength of MASM mortars was increased by up to 83% using SRCT composites. Two major mechanisms were discovered: additional hydration product formation and pore structure refinement. The results of XRD suggested that incorporating SRCT composite into MASMs increased the production of expansive sulfate-containing hydration products, such as ettringite, gypsum, and hydroxyl-Afm. The results of element mapping showed that the oxidation of pyrite in SRCTs could release sulfates into the surrounding area and participate in the hydration of MASM, indicating that SRCTs can work as an auxiliary activator for MASMs. Furthermore, the addition of SRCT significantly refined the pore structure of MASMs, leading to the reduction in porosity by up to 37.77%. These findings confirm a synergistic effect on activating the slag between SRCTs and MgO, promoting the mass utilization of SRCTs. As a result, the additional expansive hydration products contribute to the enhanced compressive strength and refined pore structure. Full article

(This article belongs to the Special Issue Microstructural, Mechanical, and Durability Characteristics of Cementitious Materials)

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18 pages, 1996 KiB

Open AccessArticle

Investigations on the Performance of Shotcrete Using Artificial Lightweight Shale Ceramsite as Coarse Aggregate

by Shengjun Hou, Fuhai Li, Huiqi Tang, Tao Wen, Zhao Chen and Hao Gao

Materials 2022, 15(10), 3528; https://doi.org/10.3390/ma15103528 - 13 May 2022

Cited by 3 | Viewed by 1901

Abstract

In this study, a type of artificial lightweight shale ceramsite (ALSC) was used as the coarse lightweight aggregate for shotcrete (LAS), of which the mechanical properties, chloride penetration ion resistance, and rebound behavior were investigated. Based on the experimental results on compressive, tensile, [...] Read more.

In this study, a type of artificial lightweight shale ceramsite (ALSC) was used as the coarse lightweight aggregate for shotcrete (LAS), of which the mechanical properties, chloride penetration ion resistance, and rebound behavior were investigated. Based on the experimental results on compressive, tensile, and bond strength, LAS meet the strength requirements, and the replacement rate of fly ash (FA) and silica fume (SF) are suggested to be kept at ~15% and 10%, respectively, to result in the best mechanical properties of LAS. Adding FA and SF to the mixture significantly improved the chloride ion penetration resistance (CPR) of LAS because of morphology effects and secondary hydration of FA and SF that lead to a denser microstructure of the mixture. The electric flux and chloride ion migration coefficient (D_RCM) of LAS decreased by 56% and 67%, respectively, with FA increasing from 0 to 10%. The electric flux and D_RCM further decreased by 71% (153C) and 66% (3.24 m²/s), respectively, with FA increasing from 10 to 20%. As 5–10% SF was further added, the electric flux and D_RCM of LAS decreased to extremely low levels; for instance, with FA = 10% and SF = 10%, D_RCM = 1.61 m²/s, and the electric flux was too small and could be ignored. The contact stresses between aggregate and shotcrete mixtures were measured to investigate the rebound trend of ALSC in shotcrete. According to the analyses of the theoretical model of the rebound behavior of aggregate in shotcrete proposed by Armelin and Banthia, because of the reduced contact stresses between ALSC and mortar and the smaller density of LAS compared with normal-weight aggregate, the rebound rate of ALSC was about half of that of normal-weight aggregate in the shooting process of the shotcrete. Full article

(This article belongs to the Special Issue Microstructural, Mechanical, and Durability Characteristics of Cementitious Materials)

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18 pages, 4408 KiB

Open AccessArticle

Effect of Various Fly Ash and Ground Granulated Blast Furnace Slag Content on Concrete Properties: Experiments and Modelling

by Zhiwei Qu, Zihao Liu, Ruizhe Si and Yingda Zhang

Materials 2022, 15(9), 3016; https://doi.org/10.3390/ma15093016 - 21 Apr 2022

Cited by 13 | Viewed by 2999

Abstract

Concrete is known as the most globally used construction material, but it releases a huge amount of greenhouse gases due to cement production. Recently, Supplementary Cementitious Materials (SCMs) such as fly ash and Ground Granulated Blast Furnace Slag (GGBFS) have been widely used [...] Read more.

Concrete is known as the most globally used construction material, but it releases a huge amount of greenhouse gases due to cement production. Recently, Supplementary Cementitious Materials (SCMs) such as fly ash and Ground Granulated Blast Furnace Slag (GGBFS) have been widely used in concrete to reduce the cement content. However, SCMs can alter the mechanical properties and time-dependent behaviors of concrete and the early age mechanical properties of concrete significantly affect the concrete cracking in the engineering field. Therefore, evaluation of the development of the mechanical properties of SCMs-based concrete is vital. In this paper, the time development of mechanical properties of concrete mixes with various fly ash and GGBFS was experimentally investigated. Four different cement replacement levels including 0%, 20%, 30%, and 40% by fly ash and GGBFS as well as ternary binders were considered. Compressive strength, splitting tensile strength, flexural strength, and elastic modulus of concrete were measured until 28 days. Three additional concrete mixes with ternary binders were also cast to investigate the early-age autogenous shrinkage development until 28 days. In addition, prediction models in existing standards were used and compared to experimental results. The comparison results showed that the prediction models overestimated the compressive strength but underestimated the splitting tensile strength development and autogenous shrinkage. As a result, a model capturing the effect of fly ash and GGBFS on the development of compressive and splitting tensile strength is proposed to improve the prediction accuracy for current standards and empirical models. Full article

(This article belongs to the Special Issue Microstructural, Mechanical, and Durability Characteristics of Cementitious Materials)

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Review

Jump to: Research

19 pages, 2568 KiB

Open AccessReview

Impact of Freeze–Thaw Cycles on the Long-Term Performance of Concrete Pavement and Related Improvement Measures: A Review

by San Luo, Tianwen Bai, Mingqin Guo, Yi Wei and Wenbo Ma

Materials 2022, 15(13), 4568; https://doi.org/10.3390/ma15134568 - 29 Jun 2022

Cited by 23 | Viewed by 3748

Abstract

Freeze–thaw damage is one of the most severe threats to the long-term performance of concrete pavement in cold regions. Currently, the freeze–thaw deterioration mechanism of concrete pavement has not been fully understood. This study summarizes the significant findings of concrete pavement freeze–thaw durability [...] Read more.

Freeze–thaw damage is one of the most severe threats to the long-term performance of concrete pavement in cold regions. Currently, the freeze–thaw deterioration mechanism of concrete pavement has not been fully understood. This study summarizes the significant findings of concrete pavement freeze–thaw durability performance, identifies existing knowledge gaps, and proposes future research needs. The concrete material deterioration mechanism under freeze–thaw cycles is first critically reviewed. Current deterioration theories mainly include the hydrostatic pressure hypothesis, osmolarity, and salt crystallization pressure hypothesis. The critical saturation degree has been proposed to depict the influence of internal saturation on freeze–thaw damage development. Meanwhile, the influence of pore solution salinity on freeze–thaw damage level has not been widely investigated. Additionally, the deterioration mechanism of the typical D-cracking that occurs in concrete pavement has not been fully understood. Following this, we investigate the coupling effect between freeze–thaw and other loading or environmental factors. It is found that external loading can accelerate the development of freeze–thaw damage, and the acceleration becomes more evident under higher stress levels. Further, deicing salts can interact with concrete during freeze–thaw cycles, generating internal pores or leading to crystalline expansion pressure. Specifically, freeze–thaw development can be mitigated under relatively low ion concentration due to increased frozen points. The interactive mechanism between external loading, environmental ions, and freeze–thaw cycles has not been fully understood. Finally, the mitigation protocols to enhance frost resistance of concrete pavement are reviewed. Besides the widely used air-entraining process, the freeze–thaw durability of concrete can also be enhanced by using fiber reinforcement, pozzolanic materials, surface strengthening, Super Absorbent Polymers (SAPs), and Phase Change Materials. This study serves as a solid base of information to understand how to enhance the freeze–thaw durability of concrete pavement. Full article

(This article belongs to the Special Issue Microstructural, Mechanical, and Durability Characteristics of Cementitious Materials)

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